Such so-called bar screen baskets are known, in particular, from EP-B-0 417 408 and DE-A-39 27 748 corresponding thereto, from EP-A-0 499 154 and DE-A-41 04 615 corresponding thereto, and from EP-A-0 705 936.
These publications describe various methods for fixing the profiled bars in the cutouts of the supporting rings, and in all these bar screen baskets the inner circumference thereof forms the inlet side for the fiber suspension to be sorted.
To produce the bar screen basket according to EP-B-0 417 408 the cutouts open at their edge are produced in initially straight or only slightly bent profiled bar supports which are later bent to form closed supporting rings. The cutouts open at their edge have such a shape that they each form an undercut at a radial spacing from the first edge of the profiled bar supports into which the cutouts open, and the cross-sectional shape of the profiled bars is adapted to the configuration of the cutouts such that a projection of the profiled bar cross section engages in this undercut, and the profiled bars are thus held positively in the cutouts and are prevented from sliding out of the cutouts transversely to the longitudinal direction of the profiled bar supports. When the profiled bar supports are then bent into closed supporting rings the resulting narrowing of the cutouts causes the profiled bars to be clamped in the cutouts of the supporting rings. Both the profiled bar supports and the supporting rings of this known bar screen basket which are finally produced from these have a cross-sectional shape corresponding to a flat rectangle.
The bar screen basket according to EP-A-0 499 154 or DE-A-41 04 615 differs from this known bar screen basket only in that the configuration of the undercuts of the cutouts of the profiled bar supports and of the projections of the profiled bars engaging in these undercuts allows the profiled bars to be introduced transversely to their longitudinal direction into the open-edged cutouts of the profiled bar supports, which results in a type of snap closure, by means of which the profiled bars are prevented from sliding out of the cutouts of the profiled bar supports again transversely to their longitudinal direction. Therefore, whereas in the manufacture of the bar screen basket according to EP-B-0 417 408 the profiled bars are pushed into the cutouts of the profiled bar supports in their longitudinal direction, in the manufacture of the bar screen basket according to EP-A-0 499 154 the profiled bars are introduced into the cutouts of the profiled bar supports transversely to the longitudinal direction of the profiled bars. In the manufacture of the bar screen basket according to EP-A-0 499 154, too, the profiled bar supports are then bent into closed supporting rings and the profiled bars are thereby clamped in the cutouts.
In the bar screen basket according to EP-A-0 705 936, the profiled bars have a T-shaped cross section and the open-edged cutouts of the supporting rings have the shape of a rectangular slot into which there is inserted in the radial direction from the inside the rib of a profiled bar forming the foot of the T-shaped cross section. Clamping rings are then placed around the supporting rings so as to compress the supporting rings and thereby decrease the diameter in the radial direction, in order to clamp the aforementioned ribs of the profiled bars in the supporting ring cutouts.
Screen baskets with quite a different diameter are used in so-called sorters for fiber suspensions for the production of paper, cardboard and the like, but for cost reasons one endeavors to always use profiled bars which have identical cross-sectional shapes and cross-sectional dimensions. In the bar screen baskets according to EP-B-0 417 408 and EP-A-0 499 154, the size of the clamping forces by means of which the profiled bars are held firmly in the supporting rings does, however, depend to quite a considerable degree upon the diameter of the supporting rings into which the profiled bar supports are formed after insertion of the profiled bars into the open-edged cutouts of the profiled bar supports, unless one were to vary the configuration or dimensions of the cutouts to be produced in the profiled bar supports in dependence upon the diameter of the bar screen basket to be produced, a measure which naturally results in an increase in the manufacturing costs--cutouts designed independently of the screen basket diameter result in clamping forces which decrease progressively as the screen basket diameter increases. Furthermore, in the manufacture of the bar screen baskets known from EP-B-0 417 408 and EP-A-0 499 154, the profiled bars may shift in the longitudinal direction of the bars relative to the profiled bar supports, which may cause an obstruction during the bending of the profiled bar supports into closed supporting rings--it is only by this bending operation that the profiled bars are clamped in the cutouts, and, of course, in a finished bar screen basket the one or other ends of all profiled bars must lie in the same plane extending perpendicularly to the screen axis.
The fixing of the profiled bars in the supporting rings disclosed in EP-A-0 705 936 is presumably problematic not only because the attachment and closure of the clamping rings pressing the supporting rings radially inwardly appears difficult if sufficiently high clamping forces are to be generated, but, in addition, this known bar screen basket also necessitates manufacture and attachment of the clamping rings.